Hybrid electric vehicles (HEVS) combine the internal combustion engine of a conventional vehicle with the battery and electric motor of an electric vehicle. This results in an increase in fuel economy over conventional vehicles. This combination also offers extended range and rapid refueling that users expect from a conventional vehicle, with a significant portion of the energy and environmental benefits of an electric vehicle. The practical benefits of HEVs include improved fuel economy and lower emissions compared to conventional vehicles. The inherent flexibility of HEVs also permits their use in a wide range of applications, from personal transportation to commercial hauling.
A parallel hybrid electric vehicle requires that a power path for both constant and variable power be present. That is, a parallel hybrid electric vehicle uses power from both a mechanical source such as an internal combustion engine as well as an electrical source. This permits the HEV to use a smaller engine as the mechanical source. The smaller engine size and system operating characteristics provide even greater performance or improved fuel economy with lower emission. A significant challenge, however, in the design of HEVs, has been to produce a drive system that takes advantage of the high efficiency of mechanical components and the versatility of electrical components.
In the past, various types of parallel hybrid systems have been proposed for multiple use applications such as automobiles. For example, planetary gear sets have been used in automatic transmissions for many years. However, most automatic transmissions use a double planetary gear set such as a Simpson or Ravigneaux set. The typical automatic transmission uses only a single power source for the vehicle. Accordingly, it is desirable to provide a drive system which allows the system to operate at its most efficient power transmission point where the system spends most of its time while providing a means of generating the torque required to accelerate the vehicle without having a multi-gear ratio transmission. It is further desirable to provide a drive system that enables each source (mechanical or electrical) in the system to operate either independently or in conjunction with one another for transferring power to an output device.
A vehicle transmission system adapted for receiving inputs from variable and constant power sources for driving an output shaft comprises a planetary gear set comprising a sun gear, a ring gear connected to the output shaft, a plurality of planet gears, and a carrier assembly rotatably supporting the plurality of planet gears journaled with the sun and ring gears. A torque transmitting arrangement is coupled to the sun gear and to the shaft of the variable power source for influencing rotation of the sun gear according to the rotation of the variable power supply shaft, thereby influencing rotation of the ring gear and the output shaft connected thereto. The carrier assembly of the planetary gear arrangement is selectively connectable to the constant power source via a clutch and brake mechanism for selectively influencing rotation of the carrier assembly of the planetary gears and the ring gear, to thereby influence rotation of the output shaft.
A vehicle transmission system having a drive shaft which can be driven continuously or at varying speeds and operable in a first mechanical mode, a second electrical mode, or a third combined mode of operation, comprises a combining planetary gear arrangement having a plurality of members and operatively coupled to a rotatable shaft of a variable power source, a rotatable shaft of a constant power source, and to the output drive shaft. A clutch and brake mechanism is operable in the first and third modes for connecting the constant power source with a member of the combining planetary gear arrangement for establishing a drive path in the combining planetary gear arrangement for influencing rotation of the output shaft according to a rotation direction of the constant power source shaft, and in the second mode for grounding the member of the combining planetary gear arrangement for preventing rotation of the output drive shaft from being influenced by the constant power source. A torque transmitting arrangement is coupled to another member of the combining planetary gear arrangement and responsive to the variable power source for influencing rotation of the output shaft according to a rotation direction of the shaft of the variable power source in the second and third modes of operation, and in the first mode of operation, for producing sufficient torque to prevent rotation of the another member for preventing rotation of the output drive shaft from being influenced by the variable power source. The variable power source is driven to a synchronizing speed to enable the transmission system to change modes.